1. Field of the Invention
This invention relates to a radiation image information detecting method and apparatus, wherein radiation image information is detected from a solid-state radiation detector, which is capable of recording image information with respect to each of pixels when radiation carrying the image information is irradiated to the solid-state radiation detector, and which is capable of outputting an image signal representing the image information having been recorded.
2. Description of the Related Art
With respect to X-ray (radiation) imaging operations for medical diagnoses, and the like, various X-ray imaging apparatuses, in which solid-state radiation detectors (utilizing semiconductors as principal sections) are utilized as X-ray image information recording means, have heretofore been proposed and used in practice. With each of the X-ray imaging apparatuses described above, X-rays carrying image information of an object is detected by the solid-state radiation detector, and an image signal representing an X-ray image of the object is thereby obtained.
As for the solid-state radiation detectors to be utilized in the X-ray imaging apparatuses, various types of solid-state radiation detectors have heretofore been proposed. For example, from the view point of an electric charge forming process for converting the X-rays into electric charges, the solid-state radiation detectors may be classified into a photo conversion type of solid-state radiation detector and a direct conversion type of solid-state radiation detector. With the photo conversion type of the solid-state radiation detector, fluorescence, which has been produced by a fluorescent substance when X-rays have been irradiated to the fluorescent substance, is detected by a photo-conductor layer, and signal electric charges having thus been generated in the photo-conductor layer are accumulated at a charge accumulating section. Also, the signal electric charges having thus been accumulated at the charge accumulating section are converted into an image signal (an electric signal), and the thus obtained image signal is outputted from the solid-state radiation detector. With the direct conversion type of the solid-state radiation detector, signal electric charges, which have been generated in a photo-conductor layer when the X-rays have been irradiated to the photo-conductor layer, are collected with a charge collecting electrode and accumulated at a charge accumulating section, the signal electric charges having thus been accumulated at the charge accumulating section are converted into an electric signal, and the thus obtained electric signal is outputted from the solid-state radiation detector. In the direct conversion type of the solid-state radiation detector, the photo-conductor layer and the charge collecting electrode constitute a principal section.
Also, from the viewpoint of an electric charge read-out process for reading out the accumulated electric charges to the exterior, the solid-state radiation detectors may be classified into an optical read-out type of solid-state radiation detector and a thin-film transistor (TFT) read-out type of solid-state radiation detector. With the optical read-out type of the solid-state radiation detector, reading light (a reading electromagnetic wave) is irradiated to the solid-state radiation detector, and electric charges having been accumulated are thereby read out. With the TFT read-out type of the solid-state radiation detector, TFT's connected to a charge accumulating section are actuated successively, and electric charges having been accumulated are thereby read out. (The TFT read-out type of the solid-state radiation detector is described in, for example, U.S. Pat. No. 6,828,539.)
The applicant proposed an improved direct conversion type of solid-state radiation detector in, for example, U.S. Pat. No. 6,268,614. The improved direct conversion type of the solid-state radiation detector is a direct conversion type and optical read-out type of a solid-state radiation detector. The improved direct conversion type of the solid-state radiation detector comprises a recording photo-conductor layer, which is capable of exhibiting photo-conductivity when recording light (the X-rays, the fluorescence produced through irradiation of the X-rays, or the like) is irradiated to the recording photo-conductor layer. The improved direct conversion type of the solid-state radiation detector also comprises a charge transporting layer, which acts approximately as an electrical insulator with respect to electric charges having a polarity identical with the polarity of latent image charges, and which acts approximately as an electrical conductor with respect to transported electric charges having a polarity opposite to the polarity of the latent image charges. The improved direct conversion type of the solid-state radiation detector further comprises a reading photo-conductor layer, which is capable of exhibiting the photo-conductivity when a reading electromagnetic wave is irradiated to the reading photo-conductor layer. The recording photo-conductor layer, the charge transporting layer, and the reading photo-conductor layer are overlaid in this order. The signal electric charges (i.e., the latent image charges) carrying image information are accumulated at an interface (i.e., a charge accumulating section) between the recording photo-conductor layer and the charge transporting layer. Also, electrodes (i.e., a first electrical conductor layer and a second electrical conductor layer) are formed on opposite sides of the combination of the three layers described above. In the improved direct conversion type of the solid-state radiation detector, the recording photo-conductor layer, the charge transporting layer, and the reading photo-conductor layer constitute a principal section.
Ordinarily, in an image signal having been acquired from each of the solid-state radiation detectors described above, an offset component has been superposed with respect to each of pixels of the solid-state radiation detector. In such cases, the problems occur in that accurate image information is not capable of being acquired. In order for the problems described above to be eliminated, it may be considered to employ a technique, wherein offset component information is acquired just before an imaging operation is performed, and wherein the image signal having been acquired with the imaging operation is corrected in accordance with the offset component information such that the offset components are removed from the image signal. However, in order for the offset component information to be acquired from all of the pixels of the solid-state radiation detector, a long time is required. Therefore, in such cases, the problems occur in that it becomes necessary for the imaging operator to wait for a long time before the imaging operation becomes possible. The problems described above are not appropriate from the view point of work flow.
Also, a method and an apparatus, wherein the offset component information with respect to the solid-state radiation detector is acquired just before the imaging operation is performed and just after the imaging operation has been performed, and wherein the image signal having been acquired with the imaging operation is corrected in accordance with the offset component information such that the offset components are removed from the image signal, have been disclosed in, for example, Japanese Unexamined Patent Publication No. 10(1998)-208016. However, it often occurs that, just after the image signal has been read out from the solid-state radiation detector, residual signal charges (i.e., residual latent image charges) remain in the solid-state radiation detector. Therefore, with the disclosed method and the disclosed apparatus, the offset components are not always capable of being acquired accurately. Further, there is a strong demand for the capability of the viewing of an acquired visible image immediately after the imaging operation has been performed. However, with the disclosed method and the disclosed apparatus, wherein it is necessary for the offset component information to be acquired just after the imaging operation has been performed, a long time is required before the viewing of the acquired visible image becomes possible, and therefore it is not possible to satisfy the aforesaid demand for the capability of the viewing of the acquired visible image immediately after the imaging operation has been performed.
An apparatus aiming at satisfying the demand for the capability of the viewing of the acquired visible image immediately after the imaging operation has been performed has been proposed in, for example, Japanese Unexamined Patent Publication No. 2003-047605. With the proposed apparatus, two independent correction tables are prepared for amplifying devices, whose offset characteristics are apt to alter with the passage of time, and for the solid-state radiation detector, whose offset characteristics are not apt to alter with the passage of time. Also, with respect to the solid-state radiation detector, which requires a long time for the acquisition of the offset component information, the offset component information is acquired previously. Further, with respect to only the amplifying devices, whose offset component information is capable of being acquired quickly, the offset component information is acquired just before the imaging operation is performed. In this manner, the acquired image signal is corrected. However, the solid-state radiation detector involves a certain degree of the alteration of the offset characteristics with the passage of time. Therefore, with the proposed apparatus, the correction of the image signal is not capable of being made accurately.